Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with agraphical user interface showing the new design;

FIG. 2 is a front view of a second embodiment thereof;

FIG. 3 is a front view of a third embodiment thereof; and,

FIG. 4 is a front view of a fourth embodiment thereof.

The broken line showing of the display screen or portion thereof, textand portions of the graphical user interface form no part of the claimeddesign.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.